1. Field of the Invention
This invention generally relates to the field of optimization of control variables to maximize production of Natural Gas Liquids (“NGL”) in a gas plant while minimizing the refrigeration system power usage, including systems in multiple processing trains.
2. Description of the Related Art
Gas plants produce fuel gas, Natural Gas Liquids (“NGL”) and other solid components such as sulfur. Such plants typically include distillation columns, heat exchangers, and refrigeration systems. The NGL product must meet certain specifications in order to be a saleable product, but variation within these boundaries is acceptable. Early efforts to improve NGL quality have been directed toward maximizing the amount of refrigeration used to achieve better recovery of heavier components. As energy costs have increased, this approach is no longer economical.
Other efforts have focused on design of turbo-expanders that drive recompression with the objective of maximizing NGL production. Other methods teach of physically manipulating the temperature profile within the column to obtain desired separation results or pressure responsive fractionation control system. With the increasing cost of energy, these approaches may not provide the most cost-effective approach.
It would be advantageous to develop a new method and apparatus that provides improvement in the recovery of the valuable NGL products while minimizing energy requirements, including systems in multiple processing trains. It would be advantageous to allow for the optimization of the process variables within allowable quality variations and equipment constraints while minimizing the overall electricity or energy usage.